Have you tried either of the following URL's:
http://192.168.4.40:8080/admin
From your debug log. The method you are using to change the lighttpd port is not sticky - it will be overwritten on the next Pi-hole update or repair.
-rw-r--r-- 1 root root 4113 Aug 15 00:59 /etc/lighttpd/lighttpd.conf
server.modules = (
"mod_access",
"mod_auth",
"mod_expire",
"mod_fastcgi",
"mod_accesslog",
"mod_compress",
"mod_redirect",
"mod_setenv",
"mod_rewrite"
)
server.document-root = "/var/www/html"
server.error-handler-404 = "/pihole/index.php"
server.upload-dirs = ( "/var/cache/lighttpd/uploads" )
server.errorlog = "/var/log/lighttpd/error.log"
server.pid-file = "/run/lighttpd.pid"
server.username = "lighttpd"
server.groupname = "lighttpd"
server.port = 8080
...
For a more permanent port change, see the following: